Method of producing an ink jet recording head

BACKGROUND OF THE INVENTION

The invention relates to an ink jet recording head in which a silicon single-crystal substrate is used for a spacer forming member, and a method of producing such an ink jet recording head.

An ink jet recording head has a pressurizing chamber formed by respectively attaching a nozzle plate in which nozzle openings are formed and an elastic plate to both faces of a spacer with an adhesive. The elastic plate is deformed by a piezoelectric vibrating element. Since the ink jet recording head of this type does not utilize a thermal energy as a driving source for ejecting ink drops, the ink quality is not thermally changed. Particularly, therefore, it is available to eject color inks which may easily be thermally deteriorated. In addition, an amount of displacement of the piezoelectric vibrating element can be adjusted so that the ink amount of each ink drop is desirably regulated. For these reasons, such a head is most suitably used for configuring a printer for color printing with a high quality.

When color printing with a higher quality is to be performed by using an ink jet recording head, higher resolution is required. As a result, sizes of a piezoelectric vibrating element, a partition wall of a spacer member, and the like are inevitably reduced so that higher precision is required in the steps of working and assembling such members.

Accordingly, it has been studied that members for an ink jet recording head are worked by adopting a parts-manufacturing technique utilizing anisotropic etching of a silicon single-crystal substrate in which minute shapes can be worked with high accuracy by a relatively easy method, i.e., a so-called micro machining technique. Various techniques and methods are proposed, for example, in Japanese Patent Application Laid-open Nos. Hei. 3-187755, Hei. 3-187756, Hei. 3-187757, Hei. 4-2790, Hei. 4-129745, and Hei. 5-62964.

When color images or characters are to be printed with a high quality, it is required not only to increase the arrangement density of nozzle openings, but also to perform the printing by a so-called area gradation in which the area of one dot is varied in accordance with an image signal. In order to perform such an area gradation, the ink amount of each ink drop in one ejecting operation must be reduced to be as small as possible, and high-speed driving must be enabled, thereby realizing a recording head by which one pixel can be printed by several ejections of ink drops.

To comply with this, first, the displacement amount of the piezoelectric vibrating element must be reduced, and the displacement must be instantaneously reflected as a volume change of a pressurizing chamber. In addition, in order to link the small volume change of the pressurizing chamber to the ejection of ink drops, it is necessary to reduce the pressure loss in the pressurizing chamber to a level as small as possible.

In order to efficiently link the displacement of the piezoelectric vibrating element to the volume change of the pressurizing chamber, it is essential to increase the rigidity of the pressurizing chamber. In order to reduce the pressure loss in the pressurizing chamber, it is essential to make the volume of the pressurizing chamber as small as possible.

In order to reduce the volume of the pressurizing chamber, it is first considered that the opening area of a spacer which forms the pressurizing chamber is reduced. In view of the working accuracy of the piezoelectric vibrating element which abuts against the spacer, the reduction is limited to about one arrangement pitch of the nozzle openings at the maximum. For this reason, the reduction of the volume must be realized by decreasing the depth of the pressurizing chamber.

In view of the handling of a spacer in the assembling step or the like, however, the spacer must have the rigidity of some extent. To comply with this, a silicon single-crystal having a thickness of at least 220 μm must be used as a silicon single-crystal substrate which constitutes the spacer. If a thin substrate having a thickness less than 220 μm, the rigidity is very low this produces a problem in that damages or unpredictable warpage may disadvantageously occur in the assembling step.

As a method of forming a shallow pressurizing chamber in a sufficiently thick silicon single-crystal substrate by anisotropic etching, it may be contemplated to use a technique in which only one face of the silicon single-crystal substrate is etched, i.e., a so-called half etching method. Since the pressurizing chamber must be communicated with a nozzle opening for ejecting ink drops, it is necessary to form a through hole which elongates from the face where a nozzle plate is provided to the pressurizing chambers.

As well known in the art, in order to form a through hole H by anisotropic etching, as shown in

FIG. 27

, it is necessary to set an opening length so as to be about 1.7 (the square root of 3) or more times as large as the thickness of the silicon single-crystal substrate. If the employed substrate has a thickness of 220 μm or more, the minimum length of the opening of the through hole is about 380 μm.

As thus constructed, the volume of a communicating hole causes the volume of the pressurizing chamber to increase. In addition, the size of the communicating hole is equal to the thickness of the silicon single-crystal substrate, i.e., 220 μm, and the length in the longitudinal direction is 380 μm. Accordingly, there arises a problem in that the opening area of the silicon single-crystal substrate is increased and eventually the rigidity of the spacer is disadvantageously degraded.

In a recording head which uses a spacer made of a silicon single-crystal substrate, a piezoelectric vibrating element

130

of the longitudinal vibration mode is used as an actuator as shown in FIG.

28

. The piezoelectric vibrating element

130

of the longitudinal vibration mode is fixed to a frame

135

together with a passage unit

134

which comprises an elastic plate

131

, a spacer

132

, and a nozzle plate

133

, so as to be assembled in an ink jet recording head.

Distortion caused by a difference in coefficients of thermal expansion between ceramic constituting the piezoelectric vibrating element

130

and a material constituting the frame

135

, in general, plastic occurs substantially in a proportional manner to the length L of the piezoelectric vibrating element

130

. When heat is applied in an adhering step so as to obtain a high adhesive strength and then the condition is returned to a normal use condition, a temperature difference of 40° C. or more occurs. In the case where the effective length L of the piezoelectric vibrating element

130

is 5.5 mm, for example, an expansion difference of about 10 μm is caused by the above-mentioned difference, so that the elastic plate

131

may be damaged. Although such a damage may not be caused, the passage unit having a relatively low rigidity is distorted by the stress caused by the difference in thermal expansion. As a result, there arises a problem in that the flying directions of ink drops go out of alignment and errors are caused in hitting positions, thereby degrading the printing quality.

SUMMARY OF THE INVENTION

The invention provides an ink jet recording head comprising: a spacer in which pressurizing chambers, an ink supply port, and a common ink chamber are formed by anisotropic etching of a silicon single-crystal substrate; a nozzle plate having nozzle openings at the same pitches as those of the pressurizing chambers; and an elastic plate which causes the pressurizing chambers to expand and contract, the nozzle plate being attached to one face of the spacer, the elastic plates being attached to the other face of the spacer. In the ink jet recording head, the pressurizing chambers are formed as recesses by half etching of the silicon single-crystal substrate, and nozzle communicating holes through which the pressurizing chambers are connected to the nozzle openings are formed as through holes each having a size smaller than a width of each of the pressurizing chambers, by full etching of the silicon single-crystal substrate. The common ink chamber is formed as a through hole by full etching of the silicon single-crystal substrate. Since each of the pressurizing chambers is formed as a recess, the volume of the pressurizing chamber is reduced to a degree as small as possible. Each of the pressurizing chambers is connected to the corresponding nozzle opening on the other face side via the nozzle communicating hole, so that the effective volume related to the ejection of ink drops is reduced. The ratio occupied by through holes is reduced so that the inherent rigidity of the silicon single-crystal substrate is effectively used.

It is a first object of the invention to provide a novel ink jet recording head in which a silicon single-crystal substrate having a thickness as large as possible is used as a base material and which comprises a pressurizing chamber having a depth smaller than a thickness of the silicon single-crystal substrate.

It is a second object of the invention to provide an ink jet recording head in which degradation of the printing quality and damages due to a difference in thermal expansion between a piezoelectric vibrating element and a head unit or a frame are prevented from occurring.

It is another object of the invention to propose a method of producing the above-mentioned ink jet recording head.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1

is a view showing one embodiment of an ink jet recording head of the invention in a section structure taken along the direction of arranging pressurizing chambers;

FIG. 2

is a view showing a pressurizing chamber of the ink jet recording head in a section structure taken along the longitudinal direction; and

FIG. 3

is a top view showing an embodiment of a spacer of the ink jet recording head.

FIGS.

4

(I) to

4

(IV) are views illustrating a method of producing the spacer in the recording head.

FIGS. 5

a

and

5

b

are views of another embodiment of the invention in a top structure of a spacer and a section structure thereof, respectively;

FIG. 6

is a view of another embodiment of the invention in a section structure of a spacer;

FIGS. 7

a

and

7

b

are views of another embodiment of the invention in a top structure of a spacer and a section structure thereof, respectively; and

FIG. 8

is a view showing a section structure of the above-mentioned spacer taken along the direction of arranging pressurizing chambers.

FIGS. 9

a

and

9

b

are views of another embodiment of the invention in a top structure of a spacer and a section structure thereof, respectively; and

FIGS. 10

a

and

10

b

are views of another embodiment of the invention in a top structure of a spacer and a section structure thereof, respectively.

FIGS.

11

(I) to

11

(IV) are views respectively illustrating other steps of forming a through hole functioning as a nozzle communicating hole by anisotropic etching.

FIGS.

12

(I) and

12

(II) are views respectively illustrating steps of forming a through hole and a nozzle communicating hole by anisotropic etching.

FIGS. 13

a

and

13

b

are views showing another embodiment of the invention in which a common ink chamber is formed as a recess, in a section structure taken along a longitudinal direction of a pressurizing chamber of a spacer, respectively.

FIGS. 14

a

and

14

b

are views showing another embodiment of the invention in which a common ink chamber is formed as a recess, in a section structure taken along a longitudinal direction of a pressurizing chamber of a spacer, respectively.

FIG. 15

a

and

FIG. 15

b

are views showing another embodiment of the invention in which a common ink chamber is formed as a recess, in a section structure taken along a longitudinal direction of a pressurizing chamber of a spacer, respectively.

FIG. 16

is a view showing an embodiment of the ink jet recording head of the invention in a section structure in the vicinity of pressurizing chambers; and

FIG. 17

is a top view showing a structure of a spacer with removing an elastic plate of the recording head.

FIGS.

18

(I) to

18

(V) are views illustrating steps of the first half of a method of producing the recording head, respectively; and

FIGS.

19

(I) to

19

(III) are views illustrating steps of the second half of the method of producing the recording head, respectively.

FIG. 20

is a section view showing an embodiment of the ink jet recording head of the invention; and

FIGS. 21

a

and

21

b

are section views showing an embodiment of a frame, in a structure of a section perpendicular to a side wall and that of a section parallel to the side wall, respectively.

FIG. 22

is a view showing a structure in the vicinity of an opening of a frame; and

FIG. 23

is a view showing an embodiment of a positioning structure using a frame of a piezoelectric vibrating element unit.

FIG. 24

is a section view showing another embodiment of the invention; and

FIG. 25

is a section view showing a positioning structure of a piezoelectric vibrating element unit in the embodiment.

FIG. 26

is a section view showing another embodiment of the invention.

FIG. 27

is a diagram showing a through hole formed by anisotropic etching of a silicon single-crystal substrate.

FIG. 28

is a diagram showing joint relationships among a piezoelectric vibrating element, a passage unit, and a frame in a prior art ink jet recording head.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

Hereinafter, embodiments of the invention shown in the figures will be described in detail.

FIGS. 1 and 2

show an embodiment of the invention in a section structure in the vicinity of pressurizing chambers

1

.

FIG. 3

shows a top structure of a spacer

2

according to the present invention. The spacer

2

is formed by subjecting anisotropic etching on a silicon single-crystal substrate used as a base material, having the surface of a predetermined crystal orientation, for example, a crystal orientation (

110

). On one face, formed are the pressurizing chamber

1

having a depth D

1

which is smaller than the thickness T

1

of the silicon single-crystal substrate constituting the spacer

2

, and an ink supply port

3

.

A common ink chamber

4

is formed as a through hole so as to be communicated with the ink supply port

3

. On one end of the pressurizing chamber

1

, a nozzle communicating hole

6

is formed for connecting the pressurizing chamber

1

to a nozzle opening

5

. In order to increase flexibility in connection to the nozzle opening

5

, a recess

8

is formed in the nozzle communicating hole

6

on the side of a nozzle plate

7

. The recess

8

is larger than the diameter φ of the inflow side of the nozzle opening

5

. The recess

8

has a width W

2

which is smaller than the width W

1

of the pressurizing chamber

1

, and has a depth D

2

which is substantially equal to the depth D

1

of the pressurizing chamber

1

and the ink supply port

3

.

The ink supply port

3

is formed as a recess having a depth which is equal to the depth D

1

of the pressurizing chamber

1

, but narrower than the pressurizing chamber. Namely, the width W

3

of the ink supply port

3

is substantially one half of the width W

1

of the pressurizing chamber

1

. According to this configuration, ink which has been pressurized in the pressurizing chamber

1

is suppressed so as not to return to the side of the common ink chamber

4

as much as possible, thereby allowing a much more amount of ink to be ejected through the nozzle opening

5

.

The pressurizing chamber

1

, the ink supply port

3

, and the recess

8

are formed by so-called half etching in which anisotropic etching is performed from one face of a silicon single-crystal substrate functioning as a base material of the spacer

2

, and the etching is stopped when the etched depths of D

1

and D

2

are attained.

The common ink chamber

4

is required to have a large opening area for covering all of the pressurizing chambers

1

arranged in one row. Thus, the common ink chamber

4

is formed as a through hole by performing anisotropic etching on both faces of the silicon single-crystal substrate.

On the other hand, the nozzle communicating hole

6

for connecting the pressurizing chamber

1

to the nozzle opening

5

of the nozzle plate

7

is formed so as to elongate in a longitudinal direction of the pressurizing chamber

1

by full etching so that a length L

1

required for passing through (L

1

is the square root of 3 times or more as much as the thickness T

1

of the silicon single-crystal substrate) is attained in the longitudinal direction of the pressurizing chamber

1

, while suppressing the width W

4

to be as small as possible.

Preferably, the thickness T

2

of a partition wall of the nozzle communicating hole

6

is larger than the width W

4

of the nozzle communicating hole

6

. If the width W

4

of the through hole constituting the nozzle communicating hole

6

is selected to be 70 μm or less, the thickness T

2

of the partition wall of the nozzle communicating hole

6

is selected to be 70 μm or more, and the depth D

1

of the pressurizing chamber

1

is selected to be 60 μm or less, for example, the compliance of the pressurizing chamber

1

can be made as small as possible. If the diameter of the nozzle opening

5

is about 25 μm, ink drops of about 10 nanogram (about 10×10

−6

mm

3

) can be ejected and they can be caused to fly at a velocity of 7 meters per second or higher in the air.

In the thus configured spacer

2

, an elastic plate

10

having a deformable thin portion

10

a

and a thick portion

10

b

for efficiently transmitting the vibration of the piezoelectric vibrating element

11

to the whole of the pressurizing chamber is fixed to the face on the side of the pressurizing chamber, and the nozzle plate

7

is fixed to the other face. These elements are assembled into a passage unit

13

. An end of the piezoelectric vibrating element

11

abuts against the thick portion

10

b

via a head frame which will be described later, so as to constitute a recording head.

In the embodiment, when a driving signal for expanding the piezoelectric vibrating element

11

is applied, the elastic plate

10

is expanded and displaced to the side of the pressurizing chamber

1

so as to cause the pressurizing chamber

1

to contract. Accordingly, ink in the pressurizing chamber

1

is pressurized and ejected as an ink drop from the nozzle opening

5

via the nozzle communicating hole

6

.

The pressurizing chamber

1

is configured so as to have the depth D

1

which is smaller than the thickness T

1

of the silicon single-crystal substrate constituting the spacer

2

, and the nozzle communicating hole

6

is formed so as to have the width W

4

which is to be as small as possible. As a result, the rigidity of the region forming the pressurizing chamber is increased. Accordingly, the expansion and contraction of the piezoelectric vibrating element

11

which is displaced by a very minute distance and which is impulsively deformed are absorbed at a reduced ratio by a wall

2

a

for partitioning the pressurizing chambers

1

. Therefore, the expansion and contraction of the piezoelectric vibrating element

11

efficiently act on the change of the volume of the pressurizing chamber

1

, and an ink drop of a small ink amount can be surely ejected at a predetermined velocity. As the rigidity of the spacer

2

is increased, the deformation of the passage unit

13

caused by the displacement of the piezoelectric vibrating element

11

is reduced. Consequently, the precision of arrival positions of ink drops can be maintained. Since the effective volume of the pressurizing chamber

1

is small, the flow of the ink accommodated therein can sufficiently follow the piezoelectric vibrating element

11

of a longitudinal vibration mode which can be driven at a high speed, with the result that the repetition frequency of ink drop ejection is increased.

According to the above-described recording head of the invention, the above-mentioned features cooperate so that, in response to a printing signal for one pixel, minute ink drops can impact against printing paper at one point, at a constant velocity, and with high positioning accuracy, thereby enabling pixels to be represented by area gradation.

Next, a method of producing the above-described passage unit

13

will be described with reference to FIGS.

4

(I) to

4

(IV).

In FIG.

4

(I), the reference numeral

20

designates a silicon single-crystal substrate having the surface of a crystal orientation (

110

) and having a thickness at which the substrate can be easily handled in an assembling step, for example, a thickness of 220 μm. On both faces thereof, etching protecting films

23

and

24

of silicon dioxide (SiO

2

) are formed. The etching protecting films

23

and

24

have windows

21

and

22

in through hole regions, i.e., in regions where the nozzle communicating hole

6

is to be formed, in the figure.

In regions corresponding to a pressurizing chamber

1

and a recess

8

for the connection to a nozzle opening

5

, thick etching protecting films

25

and

26

of silicon dioxide (SiO

2

) which can bear the formation of a through hole are formed.

Under this condition, the silicon single-crystal substrate

20

is immersed in an anisotropic etching fluid of an aqueous solution of potassium hydroxide (KOH) of a concentration of about 25 wt % which is kept at 80° C. Then, the anisotropic etching is started from both faces or the windows

21

and

22

, so as to form a through hole

25

which will serve as the common ink chamber

4

and the nozzle communicating holes

6

(FIG.

4

(II)).

Thereafter, the protecting films

23

and

24

of silicon dioxide are etched away so that etching protecting films

29

and

30

having windows

27

and

28

remain in regions which will serve as the pressurizing chamber

1

and the recesses

8

for the connection to the nozzle opening

5

(FIG.

4

(III)). Anisotropic etching is performed in the same way as described above by immersing the silicon single-crystal substrate

20

in an anisotropic etching fluid.

The etching is stopped when the anisotropic etching reaches predetermined depths D

1

and D

2

, so that a shallow recess

31

which will serve as the pressurizing chamber

1

and the ink supply port

3

is formed on one face, and a recess

32

serving as the recess

8

which will further serve as a communicating portion with the nozzle opening

5

is formed on the other face (FIG.

4

(IV)).

As a result, the pressurizing chamber

1

, the ink supply port

3

, and the recess

8

for the connection to a nozzle opening are formed as shallow recesses. In addition, the through hole

25

is formed. The through hole

25

passes through the silicon single-crystal substrate

20

from the recess

31

which is formed on one face and will serve as the pressurizing chamber

1

, to the recess

32

for the connection to the nozzle opening which is formed on the other face. The through hole

25

has the width W

4

which is smaller than the width W

1

of the pressurizing chamber

1

.

At last, the etching protecting films

29

and

30

of silicon dioxide (SiO

2

) which are no more necessary are removed away. As required, a silicon dioxide film is formed again on an entire surface. Thereafter, the elastic plate

10

is fixed to one face, and the-nozzle plate

7

is fixed to the other face with an adhesive, thereby completing the passage unit

13

.

In the embodiment, the silicon dioxide (SiO

2

) films are formed so as to have two levels of thickness. Accordingly, it is required to perform only one time the mask alignment process, with the result that relative positions of the recesses

31

and

32

with respect to the through hole

25

can be set with high accuracy.

In the embodiment, in order to increase flexibility in the connection of the nozzle opening

5

to the communicating hole

6

, the recess

8

for the connection is formed. However, the formation has no direct relationship to the function of the ink ejection, and hence the formation may be performed as required.

In the above-described embodiment, the nozzle communicating hole

6

is formed in a region which overlaps the pressurizing chamber

1

. Alternatively, as shown in

FIGS. 5

a

and

5

b

, an end

6

may be positioned outside the pressurizing chamber

1

. In the alternative, if the pressurizing chamber

1

is shortened in the longitudinal direction, the through hole can be formed without increasing the volume of the pressurizing chamber

1

. In addition, if slopes

6

a

and

6

b

are formed so as to guide the ink to the nozzle opening side, removal of air bubbles can be promoted.

In the above-described embodiment, the recess

8

for the connection to the nozzle opening

5

is formed in a limited area in the vicinity of the nozzle opening

5

. Alternatively, as shown in

FIG. 6

, a recess

35

having a width substantially equal to the width W

2

of the pressurizing chamber

1

or the width W

4

of the recess

8

may be formed. One end

35

a

of the recess

35

is communicated with the common ink chamber

4

in a similar manner as the pressurizing chamber

1

and the ink supply port

3

. The other end

35

b

of the recess extends to a region opposing the nozzle opening

5

. In the alternative, the flexibility of connection to the nozzle opening

5

is increased. In addition, the recess

35

may be utilized as a second ink supply port so that the ink supply to the pressurizing chamber

1

after the ink drop ejection is performed from both faces, i.e., the surface and the back face.

FIGS. 7

a

,

7

b

, and

8

show another embodiment of a spacer used in the ink jet recording head of the invention. In a spacer

40

, a pressurizing chamber

41

and an ink supply port

42

are formed as recesses on one face by conducting anisotropic etching of a silicon single-crystal substrate having the surface of a crystal orientation (

110

) in the same way as described above. A nozzle communicating hole

43

nozzle communicating hole

43

is a through hole which has a substantially L-like shape and which comprises portions

43

a

and

43

b

. The portion

43

a

having a width W

5

which is about one half of the width W

1

of the pressurizing chamber

41

is formed along one partition wall

41

a

of the pressurizing chamber

41

and extends from one end of the pressurizing chamber

41

on the side of the nozzle opening to a region where a nozzle opening

5

is positioned. The portion

43

b

in a region opposing the nozzle opening

5

has a width almost equal to the width of the pressurizing chamber

41

.

As described above, the nozzle communicating hole

43

corresponds to one partition wall of the pressurizing chamber

41

, and the width of the nozzle communicating hole

43

is increased at an end of the pressurizing chamber

41

on the nozzle opening side. This enables the width of the pressurizing chamber

41

to be made as small as possible, and the through hole to be formed so as to have a short length. In addition, a slope

43

d

in which the nozzle opening side is placed down is formed so that the ink smoothly flows. As a result, it is possible to prevent stagnation of air bubbles caused by stagnation of ink from occurring.

Also in the embodiment, in the same manner as the above-described embodiment, as shown in

FIG. 8

, the thickness T

3

of the wall between the nozzle communicating holes

43

is formed so as to be larger than the width W

5

of the nozzle communicating hole

43

. Preferably, the width W

5

of the through hole constituting the nozzle communicating hole

43

is selected so as to be 70 μm or less, the thickness T

3

of the wall between the nozzle communicating holes

43

is selected so as to be 70 μm or more, and the depth of the pressurizing chamber

41

formed by half etching is selected so as to be 60 μm or less. In this case, the compliance of the pressurizing chamber

41

can be made as small as possible. As a result, ink drops of about 10 nanogram (10×10

−6

mm

3

) can be ejected and caused to fly at a velocity of 7 meters or more per second from the nozzle opening having a diameter of 25 μm.

In the embodiment, one of the walls of the nozzle communicating hole

43

corresponds to the partition wall

41

a

of the pressurizing chamber

41

. Alternatively, as shown in FIGS.

9

(

a

) and

9

(

b

), both walls of through holes

43

a

are off-set parallel from partition walls

41

a

and

41

b

of the pressurizing chamber

41

to have a predetermined distance therebetween. Desirably, as shown in FIGS.

10

(

a

) arid

10

(

b

), a wall

43

c

of the nozzle opening side is tapered so that the avoidance of air bubbles is enhanced.

FIGS. 11 and 12

show other embodiments of a method of forming the nozzle communicating hole

43

, respectively. In the figures, a hole in the vicinity of the pressurizing chamber is shown by way of an example. In FIGS.

11

(I) to

11

(IV), a hatched region indicates an etching protecting film.

As for the etching protecting film specified and shown by hatching, in the pressurizing chamber, an etching protecting film

50

is formed in a region where a recess is to be formed by half etching. A narrow protecting film

51

which has a tapered end

51

a

is formed in a substantially center portion of the nozzle communicating hole

43

which is to be formed as a through hole. A protecting film

52

which narrowly elongates so as to divide the through hole is formed in a region formed so as to surround the nozzle opening. These protecting films are provided after positioned on both faces of the silicon single-crystal substrate (FIG.

11

(I)).

The silicon single-crystal substrate on which such etching protecting films are formed is immersed in an anisotropic etching fluid, and anisotropic etching is started from both faces. Regions on which the protecting films are not formed are etched away, and an end

51

a

of the region protected by the protecting film

51

is also etched away (FIG.

11

(II)). When the etching on both faces proceeds in this way to pass through the substrate, the region protected by the protecting film

51

is also etched away, and the end

51

a

thereof reaches the position of the protecting film

52

(FIG.

11

(III)). The etching is further performed so that the rear end side

51

b

of the protecting film

51

is separated from the portion protected by the protecting film

52

(FIG.

11

(IV)).

The etching protecting films

50

,

52

, and

51

b

which are left on the face to be a pressurizing chamber are removed away (FIG.

12

(I)). Thereafter, anisotropic etching is performed again. The etching is stopped when the etching reaches a depth which is optimum as the pressurizing chamber. As a result, recesses which will serve as the pressurizing chamber and an ink supply port are formed, and portions

61

and

62

which are left on the end side of the pressurizing chamber are removed away (FIG.

12

(II)).

Also in the above-described embodiment, a recess (a recess indicated by the reference numeral

35

in

FIG. 6

) is formed on the back face opposing the pressurizing chamber so as to elongate from a common ink chamber

4

to a nozzle opening

5

, thereby allowing ink from the common ink chamber

4

to be supplied to the pressurizing chamber

1

through both of the surface and back faces.

In the embodiment, the common ink chamber

4

is formed as a through hole. Alternatively, in order to further reduce the ink amount of an ink drop and to increase the rigidity so as to realize high-speed driving, it is desired that the common ink chamber

4

is formed not as a through hole but as a recess so that a bottom portion having a constant thickness is left in the spacer

2

, in the same manner as the pressurizing chamber.

Specifically, as shown in

FIGS. 13

a

and

13

b

, a first common ink chamber

71

is formed on a face opposing the elastic plate. The first common ink chamber

71

is formed as a recess which is communicated with all ink supply ports

42

connected to the respective pressurizing chambers

41

. On the face opposing the nozzle plate

7

, formed is a second common ink chamber

72

. The second common ink chamber

72

is formed as a recess which cooperates with the first common ink chamber

71

so as to ensure a volume for accommodating ink required for printing.

In order to communicate the first common ink chamber

71

with the second common ink chamber

72

, a connection hole

73

configured by a through hole is formed at an appropriate position in a region in which the first common ink chamber

71

faces the second common ink chamber

72

. The provision of the connection hole

73

increases the flowability of the ink in the first and second common ink chambers

71

and

72

.

According to the embodiment, when ink is supplied from the ink tank to either of the first common ink chamber

71

on the side of the elastic plate

10

and the second common ink chamber

72

on the side of the nozzle plate

7

, the ink flows into the other one of the common ink chamber

72

and

71

via the connection hole

73

. Thus, in accordance with the total volume of the two common ink chambers

71

and

72

, an amount of ink required for the printing can be supplied to the pressurizing chamber

41

through the ink supply port

42

only, or in a condition in which the recess

74

and the nozzle communicating hole

75

are used. The area occupied by through holes formed in the whole of the spacer

40

is reduced, so that the rigidity of the spacer

40

is increased. Therefore, the assembling process is easily performed, and additionally, the warpage of the whole recording head caused by the displacement of the piezoelectric vibrating element

11

during printing is reduced in degree so that the accuracy of the hitting positions of ink drops on the recording medium is enhanced.

In the embodiment, the recess

72

which forms the second common ink chamber

72

elongates to the vicinity of the nozzle opening. Alternatively, as shown in

FIGS. 14

a

and

14

b

, an end

72

a

of the recess may be stopped at a position in which a volume for a common ink chamber is ensured, and a nozzle connection hole

76

may be formed.

In the spacer

40

shown in

FIGS. 13

a

and

13

b

, a through hole which will serve as a nozzle communicating hole

75

, and a through hole which will serve as the connection hole

73

for connecting the fist common ink chamber

71

to the second common ink chamber

72

are first formed by anisotropic etching on both faces of a silicon single-crystal substrate. Next, recesses which will serve as the pressurizing chamber

41

, the ink supply port

42

, and the first common ink chamber

71

are formed by half etching on one face of the silicon single-crystal substrate. A recess which will serve as the second common ink chamber

72

, and a recess

76

for facilitating the connection of the nozzle communicating hole

75

to the nozzle opening

5

may be simultaneously formed by half etching on one process for the surface and the back face, or separately in different steps.

In the embodiment, the second common ink chamber

72

is provided on the side of the nozzle plate

7

. In the case where a sufficient volume can be ensured as a common ink chamber in a recess on one face, it is apparent that the common ink chamber

71

may be provided only on the face on which the pressurizing chamber

41

is formed, as shown in

FIGS. 15

a

and

15

b.

In the spacer

40

shown in

FIGS. 15

a

and

15

b

, a through hole which will serve as the nozzle communicating hole

75

is first formed by anisotropic full etching of a silicon single-crystal substrate. Then, recesses which will serve as the pressurizing chamber

41

, the ink supply port

42

, and the common ink chamber

71

are formed by anisotropic half etching on one face of the silicon single-crystal substrate. The recess

76

through which the nozzle communicating hole

75

is to be communicated with the nozzle opening

5

is thereafter formed in one process by half etching on the surface and the back face or separately by processes for the surface and the back face. According to the embodiment, only the nozzle communicating holes

75

which discretely exist constitute through holes, and hence the rigidity which is in the vicinity of the inherent rigidity of the silicon single-crystal substrate constituting the spacer

40

can be effectively used. Thus, the nozzle plate

7

can be made thinner, and the nozzle opening

5

can be made smaller.

FIGS. 16 and 17

show a section structure in the vicinity of a pressurizing chamber and a top structure of a spacer of another embodiment of an ink jet recording head of the invention, respectively. In the figures, the reference numeral

81

designates a spacer according to the present invention. In the spacer

81

, a pressurizing chamber

82

and an ink supply port

83

having a depth D

3

which is smaller than the thickness T

4

of the silicon single-crystal substrate are formed on one face of a silicon single-crystal substrate having the surface of a predetermined crystal orientation, for example, a crystal orientation (

110

). A common ink chamber

84

formed as a through hole is formed at another end of the ink supply port

83

so as to be communicated with the ink supply port. A nozzle communicating hole

86

which is a through hole for connecting the pressurizing chamber

82

to a nozzle opening

85

is formed at another end of the pressurizing chamber

82

.

The pressurizing chamber

82

and the ink supply port

83

are formed as shallow recesses by performing anisotropic etching on only one face of the silicon single-crystal substrate functioning as a base material of the spacer

81

. The common ink chamber

84

is formed as a through hole by anisotropic etching on both faces of the silicon single-crystal substrate because the opening area is large.

On the other hand, the nozzle communicating hole

86

is required to have a diameter as small as possible. Therefore, the nozzle communicating hole is opened by irradiation of laser light from a laser apparatus using copper ions. A laser using copper ions has high absorptivity with a silicon single-crystal substrate and is a pulse laser. Consequently, a hole can be gradually bored in such a manner that very thin layers are peeled one by one. As compared with the case where continuous laser light from a carbon dioxide laser apparatus is used for boring a hole, the nozzle communicating hole

6

can be formed into a cylindrical shape which has a circular section. As compared with the case where a through hole is formed by anisotropic etching, ink can be smoothly supplied to the nozzle opening

5

.

The thus configured spacer

81

is sandwiched by an elastic plate

87

on the pressurizing chamber side and a nozzle plate

88

on the other side, and they are integrally fixed to the spacer.

The elastic plate

87

comprises a vibration legion which is configured as a thin portion

87

a

, and a thick portion

87

b

for efficiently transmit the vibration of a piezoelectric vibrating element

89

to the whole of the pressurizing chamber. An end of the piezoelectric vibrating element

89

of the longitudinal vibration mode is fixed to the thick portion

87

b

. In

FIG. 16

, the reference numeral

90

designates a protecting film of a silicon dioxide film on a silicon single-crystal substrate which constitutes a spacer

81

.

In the embodiment, a through hole for connecting the nozzle opening

85

to the pressurizing chamber

82

can be formed without being affected by the rule of anisotropic etching of a silicon single-crystal substrate, and hence it is possible to determine the thickness in consideration of the rigidity which is to be provided in the spacer. Next, a method of producing the recording head will be described.

In FIGS.

18

(I) to

18

(V), the reference numeral

91

designates a silicon single-crystal substrate having the surface of a crystal orientation (

110

) and having a thickness at which the substrate can be easily handled in an assembling step, for example, a thickness of 220 μm. On at least one entire face of the substrate which is to be subjected to anisotropic etching, a silicon dioxide (SiO

2

) film

92

is formed so as to have a thickness by which the film is allowed to function as a protecting film in an etching process described later, for example, a thickness of 1 μm, by thermal oxidation in which heating is performed at 1,000° C. for about four hours under an oxide atmosphere containing water vapor (FIG.

18

(I)).

A pattern corresponding to an opening shape of the common ink chamber is formed at a position where a common ink chamber

84

is to be formed, and then subjected to exposure and development so as to provide a resist layer. An etching process using a silicon oxide etching fluid, for example, hydrofluoric acid buffer solution is performed so as to remove away a region of the silicon dioxide film

92

other than the resist layer, thereby forming windows

93

and

94

which will serve as the common ink chamber

84

(FIG.

18

(II)).

Next, the substrate

91

is immersed in an aqueous solution of potassium hydroxide (KOH) of a concentration of 25 wt % which is kept at 80° C. so that anisotropic etching is started from both faces or the windows

93

and

94

in which the silicon dioxide film

92

is removed away. When a hole is bored by the etching through the substrate

91

in this way, the formation of a through hole

95

which will serve as the common ink chamber

84

is completed (FIG.

18

(III)).

Next, a window

96

is formed by removing the silicon dioxide film

92

on one face in a region where the pressurizing chamber

82

and the ink supply port

83

are to be formed, in the same way as described above (FIG.

18

(IV)). Thereafter, anisotropic etching is performed by using the silicon oxide etching solution which is the same as described above. In this step, since the etching progresses from only one face, the etching is stopped when the etching reaches a depth which is optimum as the pressurizing chamber

82

, whereby a recess

97

is formed (FIG.

18

(V)).

A position

97

a

where the nozzle communicating hole

86

is to be formed in the recess

97

which will serve as the pressurizing chamber

82

in which the nozzle communicating hole

86

is irradiated with a laser light

98

from a copper-ion laser apparatus (FIG.

19

(I)). Since the laser light from the laser apparatus using copper ions is pulsatively excited, the silicon single-crystal substrate

91

and the silicon dioxide film

92

which are irradiated are intermittently evaporated and removed away, with the result that a through hole

99

having a small diameter required for the nozzle communicating hole

86

is bored (FIG.

10

(II)).

In a stage in which the spacer is completed, the aforementioned elastic plate

87

is bonded to an opening face of the recess

97

, and the nozzle plate

8

is bonded to the other face in such a manner that the nozzle opening

5

is communicated with the nozzle communicating hole

18

, thereby completing a passage unit

13

which is the same as described above (FIG.

10

(III)). In the thus configured passage unit

13

, the spacer is made by the silicon single-crystal substrate

91

of a thickness of 220 μm or more which can exhibit a strength sufficient for easy handling. Accordingly, warpage and bending of the elastic plate

8

and the nozzle plate

88

which may easily occur in an adhesion step for producing a head with high printing densely can be prevented from occurring as much as possible.

In order to enhance affinity to the ink in the passage and durability, the existing silicon dioxide film

92

may be removed away, and a silicon dioxide film may be formed again on the front face by a thermal oxidation method. In the embodiment, the nozzle communicating hole is formed by the radiation of laser light after the etching step. Alternatively, a nozzle communicating hole forming position of the silicon single-crystal substrate is first irradiated with laser light, so that a through hole

99

which will serve as the nozzle communicating-hole

86

is bored. Thereafter, in the steps shown in FIGS.

18

(I) to

18

(V), a through hole which will serve as the common ink chamber

4

, and recesses which will serve as the pressurizing chamber

2

and the ink supply port

3

may be formed. In addition, in the above-described embodiment, the face on the side of the recess

97

which will serve as the pressurizing chamber is irradiated with the laser light so as to form the through hole

99

. Alternatively, the face on which the nozzle plate is provided may be irradiated with laser light, whereby the through hole

99

is bored.

Next, a technique for constructing a recording head by abutting the piezoelectric vibrating element

11

against the above-mentioned passage unit

13

will be described.

FIG. 20

is a view showing a section structure of a recording head which is configured by using a frame

100

suitable for fixing the passage unit

13

and the piezoelectric vibrating element

11

.

FIGS. 21

a

and

21

b

show an embodiment of the frame

100

.

The frame

100

is formed as a cylinder having an accommodating chamber

101

for the piezoelectric vibrating element by injection molding of a polymer material or the like. An opening

102

into which the piezoelectric vibrating elements

11

are to be inserted is formed on one end of the frame

100

, and a fixing portion

103

to which the passage unit

13

is to be fixed via an adhesive layer is formed on the other end. On the same face as the fixing portion

103

, a window

104

for exposing an end

11

a

of the piezoelectric vibrating element

11

is formed. In addition, an overhang portion

105

which overhangs on the side of the window

104

and protrudes in the vicinity of the thick portion

87

b

of the elastic plate

87

is formed.

The reference numeral

106

designates grooves for injecting an adhesive. A tapered portion

106

a

for guiding the insertion of an injection needle is formed at an upper end of each groove

106

. The grooves

106

are formed so as to be symmetrical in the arrangement direction. Each of the grooves

106

downwardly elongates from the tapered portion

106

a

to the middle of the overhang portion

105

along a wall face

108

of the accommodating chamber

101

which opposes a fixing substrate

107

of a piezoelectric vibrating element unit

110

. The grooves

106

have a depth of, for example, about 0.2 mm by which the adhesive can flow into a region where the overhang portion

105

opposes an end

107

a

of the fixing substrate

107

by a capillary force. The wall face

108

of the frame

100

is formed as a slope so as to form a wedge-like gap

109

. As a result, the distance between wall face at the opening

102

and the fixing substrate

107

becomes larger.

As shown in

FIG. 23

, dummy vibrating elements

11

′ and

11

′ are disposed in the vibrating element unit

110

. The dummy vibrating elements

11

′ and

11

′ are made of the same material as that of the piezoelectric vibrating elements

11

but are formed so as to be slightly thicker than the piezoelectric vibrating elements

11

. The driving signal is not supplied to the dummy vibrating elements

11

′ and

11

′. These vibrating elements are fixed to a rear end plate

111

at regular pitches, and the rear end plate

111

is then fixed to the fixing substrate

107

. In the fixing substrate

107

, a slope

107

b

is formed in the thickness direction so that an end of the fixing substrate

107

does not protrude from the overhang portion

105

to the piezoelectric vibrating element

11

side.

Accordingly, the dummy vibrating elements

11

′ and

11

′ on both side ends are in contact with a side portion

100

a

of the opening

101

of the frame

100

when the vibration unit

110

is inserted into the frame

100

, so as to function as guiding members. As a result, the piezoelectric vibrating elements

11

can precisely abut against the thick portion

87

b

of the elastic plate

87

.

The fixing substrate

107

is desirably made of a material having a coefficient of thermal expansion which is substantially equal to that of the piezoelectric vibrating element

11

, for example, a piezoelectric material or another ceramic material. In the case where the rigidity must be ensured in order to prevent crosstalk caused by stress of expansion and contraction of the piezoelectric vibrating element

8

from occurring, the fixing substrate

107

may be made of a metal material. In

FIG. 21

a

, the reference numeral

112

designates a wall for dividing the accommodating chamber

101

of the frame into two chambers.

When a recording head is to be produced by using the thus constructed frame

100

, the frame

100

is set so that the fixing portion

103

is placed upward, and the passage unit

13

is fixed to the fixing portion

103

via an adhesive layer. Then, the frame

100

is set again so that the opening

101

is placed upward, and an adhesive is applied to the end

11

a

of the vibrating element

11

. When the vibrating element unit

110

is inserted from the opening

101

, both sides of the fixing substrate

107

are guided by the guides

108

a

on both sides of the wall face

108

(FIG.

22

), and the dummy vibrating elements

11

′ and

11

′ are downwardly guided by a side portion

10

a

of the frame. When the end

11

a

of the piezoelectric vibrating element

11

abuts against the thick portion

87

b

of the elastic plate

87

, the position of the piezoelectric vibrating element

11

along the axial direction is determined.

At the stage where the positioning is completed, a gap exists between the fixing substrate

107

and the side wall

108

, and a slight gap Δg is caused between the end

107

a

of the fixing substrate

107

and the surface of the overhang portion

105

. Under this condition, when a predetermined quantity of liquid adhesive is injected by using an injection needle or the like from the tapered portion

106

a

of the groove

106

formed on the side wall

108

, the adhesive enters the space formed by the fixing substrate

107

and the groove

106

, and then penetrates into the narrow gap Δg of the overhang portion

105

by a capillary force. The adhesive penetrating in the gap Δg is stopped by surface tension at an end of the gap Δg between the overhang portion

105

and the fixing substrate

107

by forming a meniscus. Thus, the adhesive will not flow to the elastic plate

87

. The adhesive in the groove

106

penetrates also into a gap between the fixing substrate

107

and the side wall

108

of the frame

100

by a capillary force, so that the adhesive enters between the entire face of the fixing substrate

107

and the side wall.

Under this condition, heating is performed tip to a temperature at which the curing of the adhesive is promoted, for example, 60° C. During the curing process, the frame

100

and the fixing substrate

107

are expanded based on the coefficients of thermal expansion of their respective materials. The coefficients of thermal expansion of the piezoelectric vibrating element

11

and the fixing substrate

107

are selected so as to be substantially equal to each other and the thickness Lo of the overhang portion

105

is about 1 mm. Even if the effective length L of the piezoelectric vibrating element

11

is as large as about 5.5 mm, therefore, the difference in thermal expansion per temperature difference of 40° C. can be suppressed to be as small as 1 to 2 μm. In the conventional ink jet recording head (FIG.

28

), the end portion of the piezoelectric vibrating element is fixed to the frame, and hence a difference in thermal expansion which corresponds to the effective length L=5.5 mm of the piezoelectric vibrating element is caused. The magnitude of the difference is about 5 to 10 μm which is five (5) times as large as that in the invention.

In the embodiment, the configuration for eliminating disadvantages caused by the difference in the coefficients of thermal expansion due to the difference in materials between the piezoelectric vibrating element

11

and the frame

100

has been described. A large difference exists in the coefficients of thermal expansion between the silicon single-crystal substrate constituting the spacer

81

which is the main component of the passage unit

13

and a polymer material constituting the frame

100

. If the passage unit

13

is firmly fixed to the frame

100

with an adhesive, therefore, there occurs a problem in that a stress is caused by the difference in the coefficients of thermal expansion in the plane direction of the passage unit

13

, so that warpage of the passage unit

13

degrades the printing quality.

FIG. 24

shows a further embodiment of the invention which solves such a problem. In the embodiment, a buffer or buffering member

116

having a window

115

is interposed between a fixing portion

103

of a frame

100

and a passage unit

13

, and the fixing portion

103

of the frame

100

is fixed to the passage unit

13

via the buffering member

116

with an adhesive. The buffering member

116

comprises an overhang portion

116

a

formed in such a manner that it does not interfere with displacement of an elastic plate

87

in at least a region opposing a pressurizing chamber. The overhang portion

116

a

slightly protrudes from the frame

100

to the side of the piezoelectric vibrating element

11

so as to form an adhesive face for an end

107

a

of a fixing substrate

107

of a piezoelectric vibrating element unit

110

. The end

107

a

of the fixing substrate

107

is fixed by an adhesive P. In the arrangement direction of the piezoelectric vibrating elements

11

, as shown in

FIG. 25

, dummy vibrating elements

11

′ and

11

′ are guided, and the dummy vibrating elements

11

′ and

11

′ function also as positioning members.

As a material for the buffering member

116

, used is a material having high rigidity for reinforcing the strength of the passage unit

13

in the plane direction, having a linear expansion coefficient in the middle of the linear expansion coefficient of the frame

100

and that of the silicon single-crystal substrate constituting the spacer

81

, and desirably having an ink resistant property. For example, stainless steel, specifically SUS430 having a linear expansion coefficient of 9E−6/° C. is used, and is formed into the buffering member by metal press working. As another example, a thermosetting resin may be used. The thermosetting resin can be easily worked into desired shape by injection molding. In addition, it is possible to relatively easily select a material having high rigidity and having a linear expansion coefficient in the middle of the linear expansion coefficients of the silicon single-crystal substrate constituting the spacer

81

and the frame

100

.

As described above, the buffering member

116

is interposed between the passage unit

13

and the frame

100

, so that the strength of the passage unit

13

is reinforced by the rigidity of the buffering member

116

. Furthermore, a difference in thermal expansion between the passage unit

13

and the frame

100

is reduced, so that bend and warpage of the passage unit

13

caused by a temperature variation can be prevented from occurring as much as possible, and variations in ink drop ejection performance can be suppressed.

In addition to the above-described construction, in the region opposing the common ink chamber

84

, a recess

117

may be formed on the common ink chamber side, and the region of the elastic plate

87

may be formed as a thin portion

87

c

, so that the compliance of the common ink chamber

87

is ensured. Thus, crosstalk can be more surely reduced. For reference purposes, materials, linear expansion coefficients, Young's modulus, plate thicknesses of elements constituting the recording head of the embodiment are listed in Table 1.

TABLE 1

Liner

expansion

Young's

Plate

coefficients

modulus

thickness

Materials

(E-6/° C.)

(kg/mm

2

)

(mm)

Nozzle plate

SUS316

17

19700

0.08

Spacer

Si

2

15900

0.28

Vibrator

PPS+SUS304

about 17

about 700

0.03

Frame

Liquid

38

880

2

crystal

polymer

Buffer member

SUS430

9

20400

0.7

In the embodiment shown in

FIG. 20

, the groove

106

for injecting an adhesive extends to the overhang portion

105

. Alternatively, as shown in

FIG. 26

, a groove

119

which is stopped at the overhang portion

105

may be formed. In the alternative, the adhesive first enters the groove

119

and then penetrates into a narrow wedge-like space

109

in which the upper portion is tapered and which is formed between the fixing substrate

107

and the side wall

108

, and a gap between the end

107

a

of the fixing substrate

107

and the overhang portion

105

by a capillary force, so as to spread therebetween. Accordingly, as compared with the embodiment shown in

FIG. 20

in which the groove is formed up to the overhang portion

105

, the disadvantage in that the adhesive is concentrated in the vicinity of the groove

106

(

FIG. 20

) can be eliminated as far as the flatness of the fixing substrate

107

and the overhang portion

105

is ensured. Thus, the adhesive can be surely diffused to the entire overhang portion

105

. In

FIG. 26

, the reference numeral

119

a

designates an adhesive injection port formed at the upper end of the groove

119

.

Number	Date	Country
7-251787	Sep 1995	JP
7-269191	Sep 1995	JP
7-260587	Oct 1995	JP
7-306622	Oct 1995	JP
8-170605	Jun 1996	JP

Number	Name	Date	Kind
5157420	Naka et al.	Oct 1992	A
5200768	Shibaike	Apr 1993	A
5375326	Usui et al.	Dec 1994	A
5424769	Sakai et al.	Jun 1995	A
5471232	Hosono et al.	Nov 1995	A
5592203	Thiel	Jan 1997	A
5600357	Usui et al.	Feb 1997	A
5684519	Matoba	Nov 1997	A
5697144	Mitani	Dec 1997	A
5710584	Suzuki et al.	Jan 1998	A
5752303	Thiel	May 1998	A

Number	Date	Country
573055	Dec 1993	EP
652108	May 1995	EP
738599	Oct 1996	EP
748690	Dec 1996	EP
55-109668	Aug 1980	JP
59-94495	May 1984	JP
60-8953	Mar 1985	JP
62-36478	Feb 1987	JP
63-295269	Dec 1988	JP
3-121850	May 1991	JP
3-187755	Aug 1991	JP
3-187756	Aug 1991	JP
3-187757	Aug 1991	JP
4-1052	Jan 1992	JP
4-002790	Jan 1992	JP
4-129745	Apr 1992	JP
5-62964	Mar 1993	JP
5-193129	Aug 1993	JP
5-220956	Aug 1993	JP
6-55733	Mar 1994	JP
6-91872	Apr 1994	JP
406206315	Jul 1994	JP
7-101058	Apr 1995	JP
7-164634	Jun 1995	JP
7-166374	Jun 1995	JP
7-266552	Oct 1995	JP
7-164636	Jun 1996	JP
6-8423	Jan 2003	JP

Method of producing an ink jet recording head

Information

Patent Number

Date Filed

Date Issued

Inventors

Original Assignees

Examiners

Agents

CPC

US Classifications

Field of Search

US

International Classifications

Abstract

Description

Claims

Priority Claims (5)

Parent Case Info

US Referenced Citations (11)

Foreign Referenced Citations (28)